/*
 * SPDX-License-Identifier: Apache-2.0
 *
 * The OpenSearch Contributors require contributions made to
 * this file be licensed under the Apache-2.0 license or a
 * compatible open source license.
 */

/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch licenses this file to you under
 * the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

/*
 * Modifications Copyright OpenSearch Contributors. See
 * GitHub history for details.
 */

package org.opensearch.example.customsigheuristic;

import org.opensearch.common.io.stream.StreamInput;
import org.opensearch.common.io.stream.StreamOutput;
import org.opensearch.common.xcontent.ObjectParser;
import org.opensearch.common.xcontent.XContentBuilder;
import org.opensearch.search.aggregations.bucket.terms.heuristic.SignificanceHeuristic;

import java.io.IOException;

/**
 * A simple {@linkplain SignificanceHeuristic} used an example of declaring a custom heuristic.
 */
public class SimpleHeuristic extends SignificanceHeuristic {
    public static final String NAME = "simple";
    public static final ObjectParser<SimpleHeuristic, Void> PARSER = new ObjectParser<>(NAME, SimpleHeuristic::new);

    public SimpleHeuristic() {}

    /**
     * Read from a stream.
     */
    public SimpleHeuristic(StreamInput in) throws IOException {
        // Nothing to read
    }

    @Override
    public void writeTo(StreamOutput out) throws IOException {
        // Nothing to write
    }

    @Override
    public String getWriteableName() {
        return NAME;
    }

    @Override
    public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
        builder.startObject(NAME).endObject();
        return builder;
    }

    @Override
    public int hashCode() {
        return 1;
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        return true;
    }

    /**
     * @param subsetFreq   The frequency of the term in the selected sample
     * @param subsetSize   The size of the selected sample (typically number of docs)
     * @param supersetFreq The frequency of the term in the superset from which the sample was taken
     * @param supersetSize The size of the superset from which the sample was taken  (typically number of docs)
     * @return a "significance" score
     */
    @Override
    public double getScore(long subsetFreq, long subsetSize, long supersetFreq, long supersetSize) {
        return subsetFreq / subsetSize > supersetFreq / supersetSize ? 2.0 : 1.0;
    }
}
